Now I think I coulda checked behind on the flop since I have very low fold equity against this opponent. Well of course I can't fold to his raise, but going broke would be too much of gambling imho. Unexpected check on the turn, and very weak bet on the river - was this a good spot for a bluff? All draws missed, and with storng hand he would definitely bet bigger the river, and probably the turn.

Flop: If you see this opponent rather being very aggressive and floating a lot then you could as well even Check behind there or even sometimes 4bet, although 4betting sometimes might put you into marginal spots, therefore I might like Bet/Call better.River: It should be doable, since we could easily represent the straight here or whatsoever. Although it's kinda close since we are against unknown, we will never know if he is capable of laying down his Jx type of hand and if we even isn't playing it this way. But small bet could easily mean that he is trying to block-bet.

I'd probably didn't take that risk if his fold to cbet would be like 70-80 (at least). But yeah, that's kinda marginal as he really could not know what to do with his JX hand. You can never trust an unknown